40 to 45. For Taiwan in 1964 r is calculated at 0.02929. Let us tabulate effects on the intrinsic rate of a fall of &Fy in the birth rates at the sei ages y to y + 4. These are shown in Table 4, along with the age-spe rates. For example, the table says that a drop in the birth rate to wome age 20 to 24 equal to one birth per 1,000 (AF20 = -0.001) will result drop in r of 0.000086, whereas a drop of the birth rate to women aged 4 44 of the same 0.001 will result in a drop of 0.000046. Evidently a drc the age-specific rate is about twice as consequential in the youngest as ir oldest group. TABLE 4 Effect on Intrinsic Rate r of a Fall in Age-Specific Birth Rate at the Several Ages, Taiwan 1964 Effect of a Fal of AF^on 1,OC Age.y to y + 4 Observed Age-Specific Rate Fy e-r (y + 2'/2) 5Lv c-rO;+2'/i)5Lj Klo (K = 28.4 year 15-19 0.018 0.5989 474,267 0.100AF15 20-24 0.123 0.5173 471,375 0.086AF20 25-29 0.162 0.4469 467,720 0.074AF2S 30-34 0.104 0.3861 463,505 0.063AF30 35-39 0.058 0.3334 458,333 0.054AF35 40-44 0.025 0.2880 451,428 0.046AF40 Source: Author's calculations. We should not underestimate the importance of this comparison bee of the zeros after the decimal point. A required diminution in the ultir increase results from lowering F^ by a certain amount, or from lowering by half of this amount, because half as many women are to be found al older as at the younger age. Example of the Assessment of a Fall in Fertility The relation is important in assessing a fall in fertility, for example tin Taiwan between 1964 and 1966. Table 5 shows the age-specific rates fa in important degree only beyond age 30, and at ages under 25 they rise the 2-year period. The net effect is downward, the Gross Reproduction 1 going from 2.45 to 2.32. However, the drop in the intrinsic rate r was proy isomparison of Canada and the United States for 1967 shows that the Net Reproduction Rate does not tell the whole story of replacement. Canada's NRR was slightly higher than that of the United States, 1.216 against 1.205. The Canadian girl child just born could expect to bear slightly more girl children than the United States girl child at 1967 rates. But the Canadian would marry older and have her children later within marriage; her length of generation— a measure something like the average age of childbearing-was 27.3 years against the United States 26.2 years. This means a more rapid turnover of generations in the United States.